There are no layers in SketchUp. There are tags. Untagged should be active at ALL times. ALL edges and faces should be created and left untagged. Only objects (groups, components, and images) get tags.You cannot make Untagged invisible. If you don’t want to see the imported image, select it and give it a tag in Entity Info. Then turn off that tag’s visibility.
If you want to use the same tags in multiple files, create a template that includes those tags.
Sounds like before you go any further you really should spend some time going through the Fundamentals at learn.sketchup.com